Telcos and ISPs carry packets from place to place. YouTube carries videos from place to place. That's a fairly fine distinction. The ISPs computers are being "commandeered" in exactly the same way.
Telcos and isps have terms of service and contractual provisions that allow for common carriage. They clearly and intentionally seek this status to protect themselves from liability rooted in the carriage. (Edit: in exchange for additional duties based on the special relationship formed, if I recall correctly).
Purveyors of coherent speech products derive similar but different immunity from cda section 230, with terms of service that define the relationship as distinctly not content neutral.
Accordingly there is a very differentiated line: the common carriage of goods. Common carriers do it but internet platforms do not.
Stepping back a moment, I stated before that the fee element of common carriage was not present in internet platforms but of course you can buy movies on YouTube so this is not as universally true as I said. On the other hand, try posting a snuff video to YouTube and you will see exactly why it is not a common carrier.
As I understand it, the argument is that if a web site gets to be sufficiently systemically critical to (society? Democracy?) that it should not be allowed to control its speech product. This would go a long way toward making every website 4chan, which is not an optimal outcome.
However I’m curious if I’m missing something. Is the goal here to deny, for example, LinkedIn the ability to constrain you from posting pornography? Or to constrain stack overflow from allowing you to post poor quality answers?
Companies don't choose to be common carriers if they can still be a monopoly/oligopoly without it. The reason common carrier regulations were adopted was because companies that had monopolies (some natural, some not), would use those monopolies in ways that were seen to be unfair competition.
All else equal, any company would rather pick and choose their customers rather than be forced to serve customers that they'd rather not for one reason or another.
If the customers they don’t want to serve are unwanted because their contribution doesn’t fit the market the company is seeking with its coherent speech product than its first amendment rights are being infringed when you force the carriage of the unwanted content.
Furthermore, forcing every social media platform to carry everything is just a questionable idea, regardless. I’m sure you have seen unmoderated internet. It’s not surprising that the common carrier model doesn’t fit social media platforms given that it would lead to perverse results.
